The present invention relates to a process for preparing a spherically shaped microcomposite comprising a perfluorinated ion-exchange polymer containing pendant sulfonic acid groups and/or pendant carboxylic acid groups entrapped within and highly dispersed throughout an inorganic oxide network. Due to their high surface area and acid functionality, these spherically shaped microcomposites possess wide utility as improved solid acid catalysts.
A microcomposite comprising perfluorinated ion-exchange polymers containing pendant sulfonic acid groups and/or pendant carboxylic acid groups entrapped within and highly dispersed throughout a metal oxide network and its preparation are disclosed in WO95/19222. The microcomposites described therein are irregular shaped particles which can be subject to attrition. Attrition can lead to fines which can cause problems in certain filtering processes and columns, such as clogging, pressure build up and the generation of friction. Fines can also find their way into a final product in certain applications which is undesirable.
Canadian Patent Application No. 2,103,653 describes shaped organosiloxane polycondensates in the form of macroscopic spherical particles. The polycondensates described contain no perfluorinated ion exchange polymer.
It is an object of the present invention to provide a shaped microcomposite that possesses high catalytic activity, high attrition resistance, and better handling characteristics.
The present invention provides a process for the preparation of at least one spherically shaped porous microcomposite which comprises a perfluorinated ion-exchange polymer containing pendant sulfonic and/or carboxylic acid groups entrapped within and highly dispersed throughout a network of inorganic oxide, wherein the weight percentage of the perfluorinated ion-exchange polymer in the microcomposite is from about 0.1 to about 90 percent, and wherein the size of the pores in the microcomposite is about 0.5 nm to about 75 nm; said process comprising the steps of:
(a) combining a water-miscible inorganic oxide network precursor system, a water-miscible liquid composition comprising a perfluorinated ion-exchange polymer containing pendant sulfonic and/or carboxylic acid groups, and an organic liquid to form a two phase liquid system;
(b) agitating the two phase liquid system sufficiently to sustain a dispersion of the water-miscible phase in the shape of spheres in the organic phase;
(c) allowing the inorganic oxide network precursor system to form a network of inorganic oxide to yield at least one spherically shaped porous microcomposite having the above-described properties; and
(d) recovering the at least one spherically shaped porous microcomposite.
This invention is directed to a process for preparing at least one spherically shaped porous microcomposite having a diameter of about 0.1 to about 1.0 mm, a specific surface area of about 10 to about 800 m2/g, and a specific pore volume of about 0.2 to about 3.0 cc/g. The at least one spherically shaped microcomposite comprises a perfluorinated ion-exchange polymer containing pendant sulfonic and/or carboxylic acid groups entrapped within and highly dispersed throughout a network of inorganic oxide, wherein the weight percentage of the perfluorinated ion-exchange polymer in the microcomposite is from about 0.1 to about 90 percent. The size of the pores in the microcomposite is about 0.5 nm to about 75 nm. Preferably, the pore size is about 0.5 to about 50 nm, most preferably about 0.5 to about 30 nm.
In step (a) of the process of the present invention, a water-miscible inorganic oxide network precursor system is combined with a water-miscible liquid composition comprising a perfluorinated ion-exchange polymer containing pendant sulfonic and/or carboxylic acid groups, and an organic liquid to form a two phase liquid system. Although the sequence of combining the components of the two phase liquid system is not critical, preferably the water-miscible components are contacted with each other first followed by contact with the organic liquid.
The water-miscible inorganic oxide network precursor system comprises an inorganic oxide network precursor, water and optionally a catalyst.
The xe2x80x9cinorganic oxidexe2x80x9d signifies metallic, semimetallic or other inorganic oxide compounds, including, for example, alumina, silica, titania, germania, zirconia, alumino-silicates, zirconyl-silicates, chromic oxides, germanium oxides, copper oxides, molybdenum oxides, tantalum oxides, zinc oxides, yttrium oxides, vanadium oxides, and iron oxides. Alumina, silica, titania and zirconia are preferred, and silica is most preferred. The term xe2x80x9cinorganic oxide network precursorxe2x80x9d refers to an inorganic oxide precursor or an inorganic oxide initially used in the present process to yield a network of inorganic oxide in the resultant at least one spherically shaped microcomposite. Most inorganic oxide network precursors will hydrolyze and condense into the network of inorganic oxide during the course of the present process. Other inorganic oxide network precursors exist initially as an inorganic oxide, such as colloidal silica.
In the case of silica, for example, a range of silicon alkoxides can be hydrolyzed and condensed to form the network of inorganic oxide. Such inorganic oxide network precursors as tetramethoxysilane, tetraethoxysilane, tetrapropoxysilane, tetrabutoxysilane, and any compounds under the class of organic alkoxides which in the case of silicon is represented by Si(OR)4, where R, which can be the same or different, includes methyl, ethyl, n-propyl, iso-propyl, n-butyl, sec-butyl, iso-butyl, tert-butyl can be used. Also included as an inorganic network precursor is silicon tetrachloride. Further inorganic oxide network precursors comprise organically modified silica, for example, CH3Si(OCH3)3, PhSi(OCH3)3,where Ph is phenyl, and (CH3)2Si(OCH3)2. Other inorganic oxide network precursors include metal silicates, for example, potassium silicate, sodium silicate and lithium silicate. As an alternative to using as is, the potassium, sodium or lithium ions of these metal silicates can be removed using a DOWEX(copyright) cation exchange resin (sold by Dow Chemical, Midland, Mich.), which generates polysilicic acid which gels at slightly acid to basic pH. The use of LUDOX(copyright) colloidal silica (E. I. du Pont de Nemours and Company, Wilmington, Del.) and fumed silica (CAB-O-SIL(copyright) sold by Cabot Corporation of Boston, Mass.) which can be gelled by altering pH and adjusting the concentration of the silicon species in solution will also yield a network of inorganic oxide in the spherically shaped microcomposite of the present invention. Preferred inorganic oxide network precursors for silica are tetramethoxysilane, tetraethoxysilane and sodium silicate; and a preferred inorganic oxide network precursor for alumina is aluminum tri-secbutoxide Al(OC4H9)3.
The amount of water used in the inorganic oxide network precursor system of the present process is at least sufficient for the complete hydrolysis and condensation of those inorganic oxide network precursors that are not already hydrolyzed and/or condensed. Preferably, an excess amount of water is used as compared with the stoichiometrically required amount. The amount of water required for hydrolysis depends on the rate of hydrolysis of each inorganic oxide network precursor used. Generally, hydrolysis takes place more rapidly with increasing amounts of water. Hydrolysis can begin upon contact of the inorganic oxide network precursor with the water.
The amount of water needed in the inorganic oxide network precursor system when inorganic oxides, such as colloidal silica, are used as the inorganic oxide network precursor is that which is sufficient to provide a water-miscible system upon its contact with the inorganic oxide network precursor.
Optionally, the water-miscible inorganic oxide precursor system may further comprise a catalyst. Representative examples of suitable catalysts are HCl, H3PO4, CH3COOH, NH3, NH4OH, NaOH, KOH and NR13, wherein R1 represents an alkyl group which contains 1 to 6 carbon atoms. The catalyst can be added with stirring.
The temperature during formation of the water-miscible inorganic oxide network precursor system can range from about 0xc2x0 C. to about 100xc2x0 C. Atmospheric pressure can be used.
Agitation, such as by stirring or ultrasonication, should be used, if necessary, to effect good contact of the inorganic oxide network precursor with the water and with the optional catalyst. Agitation may not be required for the formation of every inorganic oxide network precursor system.
The water-miscible liquid composition comprising a perfluorinated ion exchange polymer (PFIEP) containing pendant sulfonic acid, carboxylic acid, or sulfonic acid and carboxylic acid groups used in the present invention are well known compounds. See, for example, Waller et al., Chemtech, July 1987, pp. 438-441, and references therein, and U.S. Pat. No. 5,094,995, incorporated herein by reference. PFIEP containing pendant carboxylic groups have been described in U.S. Pat. No. 3,506,635, which is also incorporated by reference herein. Polymers discussed by J. D. Weaver et al., in Catalysis Today, 14 (1992) 195-210, are also useful in the present invention. Polymers that are suitable for use in the present invention have structures that include a substantially fluorinated carbon chain that may have attached to it side chains that are substantially fluorinated. In addition, these polymers contain sulfonic acid groups or derivatives of sulfonic acid groups, carboxylic acid groups or derivatives of carboxylic acid groups and/or mixtures of these groups. For example, copolymers of a first fluorinated vinyl monomer and a second fluorinated vinyl monomer having a pendant cation exchange group or a pendant cation exchange group precursor can be used, e.g. sulfonyl fluoride groups (SO2F) which can be subsequently hydrolyzed to sulfonic acid groups. Possible first monomers include tetrafluoroethylene (TFE), hexafluoropropylene, vinyl fluoride, vinylidine fluoride, trifluoroethylene, chlorotrifluoroethylene, perfluoro (alkyl vinyl ether), and mixtures thereof. Possible second monomers include a variety of fluorinated vinyl ethers with pendant cation exchange groups or precursor groups. Preferably, the polymer contains a sufficient number of acid groups to give an equivalent weight of from about 500 to 20,000, and most preferably from 800 to 2000. Representative of the perfluorinated polymers, for example, are those used in membranes, such as NAFION(copyright), commercially available from E. I. du Pont de Nemours and Company), and polymers, or derivatives of polymers, disclosed in U.S. Pat. Nos. 3,282,875; 4,329,435; 4,330,654; 4,358,545; 4,417,969; 4,610,762; 4,433,082; and 5,094,995. More preferably the polymer comprises a perfluorocarbon backbone and a pendant group represented by the formula xe2x80x94OCF2CF(CF3)OCF2CF2SO3X, wherein X is H, an alkali metal or NH4. Polymers of this type are disclosed in U.S. Pat. No. 3,282,875.
Typically, suitable perfluorinated polymers are derived from sulfonyl group-containing polymers having a fluorinated hydrocarbon backbone chain to which are attached the functional groups or pendant side chains which in turn carry the functional groups. Fluorocarbosulfonic acid catalysts polymers useful in preparing the spherically shaped microcomposites of the present invention have been made by Dow Chemical and are described in Catalysis Today, 14 (1992) 195-210. Other perfluorinated polymer sulfonic acid catalysts are described in Synthesis, G. I. Olah, P. S. Iyer, G. K. Surya Prakash, 513-531 (1986).
There are also several additional classes of polymer catalysts associated with metal cation ion-exchange polymers and useful in preparing the at least one spherically shaped microcomposite of the present invention. These comprise 1) a partially cation-exchanged polymer, 2) a completely cation-exchanged polymer, and 3) a cation-exchanged polymer where the metal cation is coordinated to another ligand (see U.S. Pat. No. 4,414,409, and Waller, F. J. in Polymeric Reagents and Catalysts; Ford, W. T., Ed.; ACS Symposium Series 308; American Chemical Society; Washington, D.C., 1986, Chapter 3).
Preferred PFIEP suitable for use in the present invention comprise those containing sulfonic acid groups, such as a sulfonated PFIEP prepared from a NAFION(copyright) solution. More preferred is a PFIEP prepared from resins having an equivalent weight of about 800 to 2000 comprising tetrafluoroethylene and perfluoro(3,6-dioxa-4-methyl-7-octenesulfonyl fluoride).
PFIEP are used within the context of the present invention in a liquid composition form (also commonly called solutions) which can be prepared using the process in U.S. Pat. No. 4,433,082 or Martin et al., Anal. Chem., Vol. 54, pp 1639-141(1982) incorporated by reference herein. Solvents and mixtures other than those in U.S. Pat. No. 4,433,082 and Martin et al. may also be effective in preparing the liquid composition of PFIEP. The liquid composition of PFIEP can be used directly and may be filtered through fine filters (e.g., 4-5.5 micrometers) to obtain clear, though perhaps slightly colored, solutions. The liquid compositions of PFIEP obtained by these processes can be further modified by removing a portion of the water, alcohols and any volatile organic by-products by distillation, e.g. to give a liquid composition containing water only.
Commercially available liquid compositions of perfluorinated ion-exchange polymer can also be used in the preparation of the at least one spherically shaped microcomposite of the present invention (e.g., a 5 wt % solution of a perfluorinated ion-exchange powder in a mixture of lower aliphatic alcohols and water, Cat. No. 27,470-4, Aldrich Chemical Company, Inc., 940 West Saint Paul Avenue, Milwaukee, Wis. 53233).
Optionally, the liquid composition comprising PFIEP may further comprise an acid or base catalyst. The catalyst acts to allow network formation of the water-miscible inorganic oxide network precursor system via gelation to occur, and/or it increases the rate of gelation once in the presence of the water-miscible inorganic oxide network precursor system.
Formation of the liquid composition comprising PFIEP can be made at a temperature ranging from about 0xc2x0 C. to about 100xc2x0 C. Atmospheric pressure can be used. Some agitation may be required to obtain good contact between the liquid composition of PFIEP and the catalyst that can optionally be added.
If the water-miscible inorganic oxide network precursor system and the water-miscible liquid composition comprising PFIEP are first contacted together prior to their combination with the organic liquid, some agitation may be required to obtain good contact between these components.
The organic liquid combined with the water-miscible inorganic oxide network precursor system and the water-miscible liquid composition comprising PFIEP in step (a) does not solubilize either the water-miscible inorganic oxide network precursor system (which may be hydrolyzed and/or condensed) or the water-miscible liquid composition of PFIEP. The result of the combination of the organic liquid, the water-miscible mixture inorganic oxide network precursor system and water-miscible liquid composition comprising PFIEP is a two phase liquid system, one phase being the organic liquid and the other phase comprising the water-miscible inorganic oxide network precursor system and the water-miscible liquid composition comprising PFIEP. The amount of organic liquid used can be 10 to 2000%, preferably 25 to 1000% by weight, with reference to the total amount of inorganic oxide network precursor used. Assessment of the amount of organic liquid used also depends in particular on what particle size is being sought for each spherically shaped microcomposite. Generally, less organic liquid is used for coarse particles (spheres with a larger diameter) and more is used for fine particles (spheres with a smaller diameter).
Suitable organic liquids are, e.g. hydrocarbons with 4 to about 40 carbon atoms, such as long chain aliphatic compounds, aromatic compounds or mixtures of aromatic compounds substituted with one or more alkyl groups, e.g. toluene or xylene isomers (separately or in a mixture); chlorinated or fluorinated hydrocarbons; linear or branched alcohols with 6 to 18 carbon atoms; phenols; dialkyl ethers which can be linear or branched, symmetric or asymmetric; di- or tri-ethers (such as dimethyl ether); and ketones which can be symmetric or asymmetric and are predominantly immiscible with water. Preferably, the organic liquid is toluene or o-, m- or p-xylene, separately or as a mixture, or mesitylene, kerosene or cumene.
In step (b) of the present process, the two phase liquid system is agitated sufficiently to sustain a dispersion of the water-miscible phase in the shape of spheres in the organic phase. The temperature at which dispersion of the second water-miscible mixture in the organic liquid is performed and spherical solids are formed from this dispersed phase, generally ranges from about 0xc2x0 C. to about 100xc2x0 C.
In step (c) of the present process, the water-miscible inorganic oxide network precursor system is allowed to form a network of inorganic oxide. Network formation is accomplished via gelation of the water-miscible inorganic oxide network precursor system which may in some instances self-initiate due to the presence of the water. In other instances, network formation is allowed by initiating gelation, which can be achieved in a number of ways depending on the PFIEP and the inorganic oxide network precursor selected. Initiation of gelation and the rate of gelation are dependent on a number of factors, such as the amount of water present, pH and the nature of any acid or base used, temperature, pressure, and concentration of the inorganic oxide network precursor. The time required for the network formation can thus vary widely depending on these factors from practically instantaneous to several days.
As discussed above, a larger amount of water can increase the rate of hydrolysis and thus the eventual rate of gelation. However, more water can slow down the rate of gelation when colloidal silica is used because of the dilution factor. A higher concentration of the inorganic oxide network precursor can result in a faster rate of gelation.
Gelation can be carried out over a wide range of acidity and basicity. Network formation can be formed by acid catalyzed gelation (see Sol-Gel Science, Brinker, C. J. and Scherer, G. W., Academic Press, 1990). Although gels can be formed using acid only, the rate of gelation is usually slower when acids are used. Representative examples of suitable catalysts are HCl, H3PO4, CH3COOH, NH3, NH4OH, NaOH, KOH and NR13, wherein R1 represents an alkyl group which contains 1 to 6 carbon atoms. Preferably, a suitable base, such as sodium hydroxide, lithium hydroxide, ammonia, ammonium hydroxide, and organic amines, such as pyridine, are used. The pH adjustment using either acid or base can be achieved in a number of ways and is also dependent on the concentration of acid or base employed. In order to allow network formation to occur, the acid or base can be contacted with either the water-miscible inorganic oxide network precursor system or with the water-miscible liquid composition comprising PFIEP prior to their combination with the organic liquid, or the acid or base can be added to the two-phase liquid system. Some hydrolysis and condensation may occur prior to the formation of the two phase system. However, network formation should be avoided until the three primary components, the water-miscible inorganic oxide network precursor system, the water-miscible liquid composition comprising PFIEP and the organic liquid, of the two phase system are combined and agitated. Thus, preferably, any needed catalyst is added after formation of the two-phase system to allow network formation to occur.
Gelation can be carried out at virtually any temperature at which the water-miscible phase is initially in liquid form. The reaction is typically carried out at room temperature. Raising the temperature can increase the rate of gelation.
Gelling may be initiated at atmospheric pressure or at an excess pressure which corresponds to the sum of the partial pressures of the components of the reaction mixture at the particular temperature being applied. The use of atmospheric pressure is preferred.
After formation, the at least one spherically shaped microcomposite, in the presence or absence of the organic liquid, may optionally be allowed to stand for a period of time. This is referred to as aging. Aging of the wet spherically shaped microcomposite for a few hours to about two (2) days at about room temperature to about 200xc2x0 C., preferably about 75xc2x0 C., leads to an increase in pore size and pore volume. This effect is characteristic of silica type gels, where the aging effect gives rise to an increasingly crosslinked network which upon drying is more resistant to shrinkage and thus a higher pore size and higher pore volume results (see, for example, the text Sol-Gel Science, Brinker, C. J. and Scherer, G. W., Academic Press, 1990, pp.518-523).
In step (d), the solid, at least one spherically shaped porous microcomposite formed is recovered from the organic liquid after a sufficient reaction time, at a temperature ranging from room temperature to about 250xc2x0 C. A sufficient reaction time is the time needed for the sphere to harden sufficiently to maintain its shape when recovered. Recovery of the moist microcomposite sphere from the organic liquid can be accomplished by decanting, filtering or centrifuging.
The spheres can be optionally purified by extraction using azeotropic distillation, i.e. removing the water from the spherically shaped microcomposite and replacing it with an organic solvent, such as an alcohol. This distilled microcomposite may then be further treated hydrothermally. Azeotropic distillation may take place prior to or after recovery of the spherically shaped microcoposite.
After recovery and optional aging, the spherically shaped microcomposites can be optionally dried at a temperature ranging from room temperature to about 250xc2x0 C., optionally under a protective gas or under vacuum, for a time sufficient to further harden and stabilize the spherically shaped microcomposites. Drying can take place from about 1 hour to about one week.
Preferably, following removal of the organic liquid, the present process further comprises reacidification, washing, filtering or a combination thereof, of the spherically shaped microcomposite. Reacidification, washing, filtering or a combination thereof, may be repeated a number of times. Reacidification of the spherically shaped microcomposite converts, for example, the sodium salt of the perfluorosulfonic acid into the acidic, active form. Suitable acids used for reacidification comprise HCl, H2SO4 and nitric acid. Washing can be done with deionized water, and the filtering removes excess acid Reacidification, washing, filtering, or a combination thereof can take place at a temperature ranging from room temperature to about 100xc2x0 C. at atmospheric pressure, and for a time ranging from about one hour to about 24 hours.
A number of reaction variables, for example pH, temperature, aging, method of drying and drying time, have been found to affect the pore size and pore size distribution of the spherically shaped microcomposite. Both higher pH and longer aging of the spherically shaped microcomposite (before solvent removal) lead to larger final pore size in dried spherically shaped microcomposites.
The porous nature of the spherically shaped microcomposite can be readily demonstrated, for example, by solvent absorption. The spherically shaped microcomposite can be observed to emit bubbles which are evolved due to the displacement of the air from within the porous network.
It is believed that the spherically shaped microcomposites of the present invention comprise a continuous network of inorganic oxide having connected porous channels which entraps a highly dispersed PFIEP within and throughout the network. The distribution of the PFIEP entrapped within and throughout the network of inorganic oxide is on a very fine sub-micron scale. The distribution can be investigated using electron microscopy, with energy dispersive X-ray analysis, which provides for the analysis of the elements Si and O (when using silica, for example) and C and F from the PFIEP. The distribution of PFIEP within a spherically shaped microcomposite of the present invention is very uniform.
The spherically shaped microcomposites of the present invention are useful as ion exchange resins, and as catalysts, for example, for alkylating aliphatic or aromatic hydrocarbons, such as the alkylation of naphthalene with propylene; for decomposing organic hydroperoxides, such as cumene hydroperoxide; for sulfonating or nitrating organic compounds; and for oxyalkylating hydroxylic compounds. Other catalytic applications for the spherically shaped microcomposites of the present invention comprise hydrocarbon isomerization and polymerization, such as the isomerization of 1 -butene to 2-butenes; carbonylation and carboxylation reactions; hydrolysis and condensation reactions; esterifications and etherifications; hydrations and oxidations; oligomerizations; aromatic acylation; aromatic benzylation; and isomerization and metathesis reactions.
The spherically shaped microcomposite can be used as a catalyst in the isomerization of an olefin. Olefin isomerization is useful in converting compounds into isomers more useful for particular applications. Olefins with the double bond at a terminal end tend to be more reactive and are easy to oxidize which can cause problems with storage. Therefore, a shift to a more stable olefin form can be desirable.
Olefin isomerization processes can be directed towards either skeletal isomerization, double bond isomerization or geometric isomerization. The spherically shaped microcomposite of the present invention can be used as a catalyst for double bond isomerization and some geometric isomerization. Skeletal isomerization is provided to a limited degree at higher temperatures utilizing the spherically shaped microcomposite of the present invention.
The spherically shaped microcomposite can be used as a catalyst with olefins such as C4 to C40 hydrocarbons having at least one double bond, the double bond(s) being located at a terminal end, an internal position or at both a terminal and internal position. Most preferred olefins have 4 to 20 carbon atoms. The olefin can be straight-chained (normal) or branched and may be a primary or secondary olefin and thus substituted with one or more groups that do not interfere with the isomerization reaction. Such substituted groups that do not interfere with the isomerization reaction could include alkyl, aryl, halide, alkoxy, esters, ethers, or thioethers. Groups that may interfere with the process would be alcohols, carboxylic acids, amines, aldehydes and ketones.
The spherically shaped microcomposite is contacted with the olefin in a fixed-bed system, a moving-bed system, a fluidized-bed system, or in a batch-type operation. This contacting can be in the liquid phase, a mixed vapor-liquid phase, or a vapor phase, in the absence of hydrogen or in the presence of hydrogen in a molar ratio of hydrogen to olefin of from about 0.01 to about 10. Inert diluents such as helium, nitrogen, argon, methane, ethane and the like can be present either in association with hydrogen or in the absence of hydrogen.
Isomerization conditions using the present spherically shaped microcomposite comprise reaction temperatures generally in the range of about 0xc2x0 C. to about 300xc2x0 C., preferably from about 24xc2x0 C. to about 250xc2x0 C. Pressure can range from ambient for gas phase or a pressure sufficient to keep reaction in the liquid phase. Reactor operating pressures usually will range from about one atmosphere to about 100 atmospheres, preferably from about one atmosphere to about 50 atmospheres. The amount of catalyst in the reactor will provide an overall weight hourly space velocity (WHSV) of from about 0.1 to 100 hrxe2x88x921, preferably from about 0.1 to 10 hrxe2x88x921; most preferably 0.1 to 2 hrxe2x88x921.
Long contact time during olefin isomerization can create undesirable by-products, such as oligomers. Short contact times ranging from about 0.01 hr to about 10 hrs; preferably 0.1 hr to about 5 hrs can be used with the present spherically shaped microcomposite. Contact time may be reduced at higher temperatures.
Any product recovery scheme known in the art can be used to isolate the resultant olefins. Typically, the reactor effluent will be condensed and the hydrogen and inerts removed therefrom by flash separation. The condensed liquid product then is fractionated to remove light materials from the liquid product. The selected isomers may be separated from the liquid product by adsorption, fractionated, or extraction.